Skyhook (structure)

A skyhook is a proposed momentum exchange tether that aims to reduce the cost of placing payloads into low Earth orbit.

Different synchronous non-rotating orbiting skyhook concepts and versions have been proposed, starting with Isaacs in 1966,[1][2] Artsutanov in 1967,[3][4] Pearson[5] and Colombo in 1975,[6] Kalaghan in 1978,[7] and Braginski in 1985.

[11] In 2000 and 2001, Boeing Phantom Works, with a grant from NASA Institute for Advanced Concepts, performed a detailed study of the engineering and commercial feasibility of various skyhook designs.

They studied in detail a specific variant of this concept, called "Hypersonic Airplane Space Tether Orbital Launch System" or HASTOL.

This would give the tip a ground speed of 3.6 km/s (Mach 10), which would be matched by a hypersonic airplane carrying the payload module, with transfer at an altitude of 100 km.

The authors stated: The primary message we want to leave with the Reader is: "We don't need magic materials like 'Buckminster-Fuller-carbon-nanotubes' to make the space tether facility for a HASTOL system.

In particular, there was concern that a bare Spectra 2000 tether would be rapidly eroded by atomic oxygen; this component was given a technology readiness level of 2.

How a rotating and non-rotating skyhook would appear in orbit
The rotating concept. If the orbital velocity and the tether rotation rate are synchronized, the tether tip moves in a cycloid curve. At the lowest point it is momentarily stationary with respect to the ground, where it can 'hook' a payload and swing it into orbit.